Method and system for detecting trouble in two-way single-fiber optical transmission

Abstract

A method for detecting trouble occurring in a single-fiber two-way optical transmission system containing first and second optical terminal stations connected to each other through at least one two-way single optical fiber. A first abnormality in a first optical signal received at the first optical terminal station is detected. A notice that the first optical terminal station will stop transmission of optical signals, is transmitted from the first optical terminal station to the second optical terminal station after occurrence of the first abnormality is detected. Transmission of optical signals from the first optical terminal station is stopped after transmission of the notice. An abnormality in an optical signal next received at the first optical terminal station is detected after the stopping of the transmission of optical signals from the first optical terminal station.

I claim: 
     
       1. A method for detecting trouble occurring in a single-fiber two-way optical transmission system containing first and second optical terminal stations connected to each other through at least one two-way single optical fiber, comprising the steps of: (a) detecting a first abnormality in a first optical signal received at the first optical terminal station;   (b) transmitting from the first optical terminal station to the second optical terminal station a first notice that the first optical terminal station will stop transmission of second optical signals when the first abnormality is detected in step (a);   (c) stopping transmission of the second optical signals from the first optical terminal station, after the transmission of the first notice in step (b); and   (d) detecting a second abnormality in a third optical signal received at the first optical terminal station after the stopping of the transmission of the second optical signals.   
     
     
       2. A method according to claim 1, further comprising the step of, (e) transmitting from the first optical terminal station to the second optical terminal station a second notice that the first optical terminal station has restarted transmission of second optical signals, after the detection of the second abnormality in step (d).   
     
     
       3. A method according to claim 2, further comprising the steps of, (f) receiving by the second optical terminal station the first notice transmitted from the first optical terminal station; and   (g) transmitting third optical signals from the second optical terminal station to the first optical terminal station after the reception of the first notice by the second optical terminal station at least until the second notice is received by the second optical terminal station.   
     
     
       4. A method according to claim 3, wherein, in step (c), the operation of stopping the transmission from the first optical station is performed a first predetermined time after the transmission of the first notice in step (b), where the first predetermined time is determined to be larger than a time needed for the second optical terminal station to receive the first notice, and to perform an operation in response to the reception of the first notice after the first notice is transmitted from the first optical terminal station in step (b). 
     
     
       5. A method according to claim 1, further comprising the step of, (h) transmitting from the first optical terminal station to the second optical terminal station alarm information indicating detection of the second abnormality detected in the first optical terminal station, after the detection of the second abnormality in step (d).   
     
     
       6. A method according to claim 1, further comprising the steps of: (i) detecting a third abnormality in a fourth optical signal received at the second optical terminal station;   (j) transmitting from the second optical terminal station to the first optical terminal station a third notice that the second optical terminal station will stop transmission of fifth optical signals, a second predetermined time after the third abnormality is detected in step (i), where the second predetermined time is determined to be larger than an elapsed time after the first abnormality is detected in step (a) until the first optical terminal station detects the second abnormality in step (d);   (k) stopping the transmission of the fifth optical signals after the transmission of the third notice in step (j); and   (l) detecting a fourth abnormality in a sixth optical signal received at the second optical terminal station after the stopping of the transmission of the fifth optical signals.   
     
     
       7. A method according to claim 6, further comprising the step of, (m) transmitting from the second optical terminal station to the first optical terminal station a fourth notice that the second optical terminal station has restarted transmission of the fifth optical signals, after the detection of the fourth abnormality in step (l).   
     
     
       8. A method according to claim 7, further comprising the step of, (n) receiving by the first optical terminal station the third notice transmitted from the second optical terminal station; and   (o) transmitting seventh optical signals from the first optical terminal station to the second optical terminal station after the reception of the third notice by the first optical terminal station until the fourth notice is received by the first optical terminal station.   
     
     
       9. A method according to claim 8, wherein, in step (k), the detection of the fourth abnormality in step (l) is performed a third predetermined time after the transmission of the third notice in step (j), the third predetermined time is determined to be larger than a time needed for the first optical terminal station to receive the third notice, and to perform an operation in response to the reception of the third notice after the third notice is transmitted from the second optical terminal station in step (j). 
     
     
       10. A method according to claim 9, wherein said operation in response to the reception of the third notice may include an operation of masking the result of the detection of the third abnormality in step (i). 
     
     
       11. A method according to claim 9, wherein said operation in response to the reception of the third notice may include an operation of halting the operation of step (j). 
     
     
       12. A method according to claim 6, further comprising the step of, (p) transmitting from the second optical terminal station to the first optical terminal station alarm information indicating the fourth abnormality detected in the second optical terminal station, after the detection of the fourth abnormality in step (l).   
     
     
       13. A system for detecting trouble occurring in a single-fiber two-way optical transmission system containing first and second optical terminal stations connected to each other through at least one two-way single optical fiber, each of the first and second optical terminal stations comprising: abnormality detecting means for detecting a first abnormality in a first optical signal received at said each optical terminal station;   notice transmitting means for transmitting from each said optical terminal station to the other optical terminal station a first notice that each said optical terminal station will stop transmission of second optical signals when the first abnormality is detected by the abnormality detecting means of the optical terminal station;   transmission stopping means for stopping the transmission of second optical signals after transmission of the first notice by the notice transmitting means;   said abnormality detecting means being able to detect a second abnormality in a third optical signal received at said each optical terminal station after the stopping of the transmission of the second optical signals.   
     
     
       14. A system according to claim 13, wherein said notice transmitting means for transmitting from each said optical terminal station to said other optical terminal station transmits a second notice that each said optical terminal station has restarted transmission of second optical signals, after detection of the second abnormality by the abnormality detecting means.   
     
     
       15. A system according to claim 14, wherein each said optical terminal station further comprises, notice receiving means for receiving the first notice transmitted from the notice transmitting means in said other optical terminal station; and   transmission continuing means for transmitting third optical signals from each said optical terminal station to said other optical terminal station after the reception of the first notice by the notice receiving means until the second notice transmitted from the notice transmitting means in said other optical terminal station is received by each said optical terminal station.   
     
     
       16. A system according to claim 15, wherein, the operation of the transmission stopping means is performed a first predetermined time after the transmission of the first notice by the notice transmitting means, the first predetermined time is determined to be larger than a total time needed for the first notice transmitted from each said optical terminal equipment to be received and recognized by said other optical terminal equipment, and for said other optical terminal station to perform an operation in response to the reception of the first notice. 
     
     
       17. A system according to claim 16, wherein said operation in response to the reception of the first notice includes an operation of masking the result of the detection of the third abnormality by the abnormality detecting means. 
     
     
       18. A system according to claim 16, wherein said operation in response to the reception of the first notice includes an operation of halting the operation of the first notice transmitting means. 
     
     
       19. A system according to claim 13, wherein said each optical terminal station further comprises, alarm information transmitting means for transmitting from each said optical terminal station to said other optical terminal station alarm information indicating the second abnormality detected in said each optical terminal station, after the detection of the second abnormality by the abnormality detecting means of said each optical terminal station.   
     
     
       20. A system according to claim 13, wherein, in one of the optical terminal stations, the notice transmitting means transmits the first notice a second predetermined time after the first abnormality is detected by the abnormality detecting means of said one of the optical terminal stations, the second predetermined time in the notice transmitting means of said one of the optical terminal stations is determined to be larger than an elapsed time after the first abnormality is detected in the abnormality detecting means of the other one of the optical terminal stations until the abnormality detecting means of said other one of the optical terminal stations detects the second abnormality of said other one of the optical terminal stations. 
     
     
       21. Terminal equipment used in an optical terminal station in a single-fiber two-way optical transmission system which contains the optical terminal station, another optical terminal station, and at least one two-way single optical fiber connecting the terminal equipment with said other optical terminal station, comprising: abnormality detecting means for detecting a first abnormality in a first optical signal received at said terminal equipment;   first notice transmitting means for transmitting from said terminal equipment to said other optical terminal station a first notice that said optical terminal station will stop transmission of second optical signals when the first abnormality is detected by the abnormality detecting means;   transmission stopping means for stopping the transmission of the second optical signals after the transmission of the first notice by the first notice transmitting means;   said abnormality detecting means being able to detect a second abnormality in a third optical signal received at said terminal equipment after the stopping of the transmission of the second optical signals.   
     
     
       22. Terminal equipment according to claim 21, further comprising second notice transmitting means for transmitting from said terminal equipment to said other optical terminal station a second notice that said terminal equipment has restarted transmission of the second optical signals, after the detection of the second abnormality by the second abnormality detecting means. 
     
     
       23. Terminal equipment according to claim 22, further comprising, first notice receiving means for receiving the first notice transmitted from said other optical terminal station; and   transmission continuing means for transmitting third optical signals from said terminal equipment to said other optical terminal station after the reception of the first notice by the first notice receiving means until the second notice transmitted from said other optical terminal station is received by said terminal equipment.   
     
     
       24. Terminal equipment according to claim 23, wherein the operation of the transmission stopping means is performed a first predetermined time after the transmission of the first notice by the first notice transmitting means, the first predetermined time is determined to be larger than a total time needed for the first notice transmitted from said optical terminal equipment to be received and recognized by said other optical terminal station, and for said other optical terminal station to perform an operation in response to the reception of the first notice. 
     
     
       25. Terminal equipment according to claim 24, wherein said operation in response to the reception of the first notice includes an operation of masking the result of the detection of the first abnormality by the abnormality detecting means. 
     
     
       26. Terminal equipment according to claim 24, wherein said operation in response to the reception of the first notice includes an operation of halting the operation of the first notice transmitting means. 
     
     
       27. Terminal equipment according to claim 21, further comprising, alarm information transmitting means for transmitting from said terminal equipment to said other optical terminal station alarm information indicating the second abnormality detected in said terminal equipment, after the detection of the second abnormality by the abnormality detecting means.   
     
     
       28. Terminal equipment according to claim 21, wherein the first notice transmitting means transmits the first notice a first predetermined time after the first abnormality is detected by the abnormality detecting means of the optical terminal station, and the first predetermined time can be preset in advance before using of terminal equipment in the single-fiber two-way optical transmission system.